WO2006057348A1 - Method for producing surface-treated silver-containing powder and silver paste using surface-treated silver-containing powder - Google Patents

Abstract

Disclosed is a method for producing a surface-treated silver-containing powder wherein a dispersion liquid, which is obtained by dispersing silver or silver compound particles (a) in a solvent together with a surfactant (b) of alkylamine type, alkylamine salt type or phosphate type having a phosphorus content of 0.5-10% by mass, is subjected to vacuum freeze drying for having the surfactant (b) adsorbed on the surfaces of the silver or silver compound particles (a), thereby producing a silver-containing powder (c) whose surface is treated with the surfactant (b). Also disclosed is a silver paste produced by dispersing the surface-treated silver-containing powder (c) in a solvent or in a solvent and a resin.

Description

 Specification

 Method for producing surface-treated silver-containing powder, and silver paste using surface-treated silver-containing powder

 Technical field

 [0001] The present invention relates to a method for producing a surface-treated silver-containing powder that can be used for printed wiring used in electronic equipment and the like and is used for a silver paste having excellent conductivity and printing accuracy. More specifically, the present invention relates to a silver paste containing the surface-treated silver-containing powder as a conductive powder component.

 In the present invention, “surface-treated silver-containing powder” includes “surface-treated silver powder” and “surface-treated silver compound powder”.

 Background art

 [0002] A conductive paste is a paste containing conductive fine particles in a solid content. Generally, metals such as gold, platinum, silver, and palladium that do not oxidize in air are used as the conductive particles. Conventionally, conductive pastes can be broadly divided into: (1) high conductivity by the fusion of silver particles, but high-temperature firing type conductive base where the base material is limited to ceramics, etc. (2) Although the power of glass and epoxy printed circuit boards can be widely applied to films, the electrical resistance is relatively high to obtain conduction through contact between metal particles due to heat shrinkage during binder curing, and polymer-type conductivity There is a paste.

 For example, when a conductive circuit is formed on a flexible printed circuit board support using a polymer-type conductive paste, the polymer-type conductive paste is screen printed on a plastic film such as polyethylene terephthalate or polyimide. Then, a conductive circuit pattern is formed, and the binder in the formed pattern coating film is cured by heating to improve conductivity and durability, and to ensure adhesion on the film.

[0003] In particular, polymer-type conductive pastes using silver or silver-based compounds are easy to achieve stable conductivity and have good heat conduction characteristics, and therefore various wiring inside or between electronic components. It is used to form electronic circuit patterns.

In the printing process of conductive circuit patterns, the printing accuracy increases with the miniaturization of circuits. Force required to increase as much as possible The accuracy is limited by the average particle size of the conductive particles. For this reason, in order to obtain good printing accuracy, the conductive particles in the conductive paste are dispersed to the primary particles, and the primary particles are completely covered with the resin, that is, highly dispersed. It is required to be in the state that has been made.

 If the highly dispersed primary particles are not sufficiently coated with resin or the like, the particles become more active as the particle diameter becomes more vigorous, so the particles in the conductive paste may aggregate, If the viscosity increases with time or is extremely extreme, gelling may occur.

 [0004] As described above, in order to form a fine wiring pattern with high accuracy and stability, it is necessary that the conductive particles are stably dispersed to the primary particles and then each particle is coated with a resin. . On the other hand, if the resin coating around the conductive particles is too thick, the resin component remaining between the particles tends to hinder the electrical conduction between the particles, so that good conductivity tends not to be obtained. This tendency becomes more remarkable as the particle size force of the conductive particles becomes smaller.

 Therefore, the amount of the resin used for dispersion and covering the surface of the conductive particles is preferably the minimum required, and the amount of the resin is less than the required amount, and the dispersibility of the conductive particles, the adhesion of the conductive paste to the substrate, It is preferable that the film formability is good.

 [0005] Conventionally, in preparing conductive paste by dispersing conductive particles in a resin, in order to improve the dispersibility, higher fatty acid ethylene oxide, or propylene oxide-added ester compound, sorbitan and fatty acid Nonionic dispersants such as ester compounds, ethylene oxide of polyhydric alcohols such as sorbitan, or ether compounds with propylene oxide, ethylene oxide of alkylbenzene, or propylene oxide adducts, alkylbenzene Sulfonic acid alkali salts, higher alcohol sulfate alkaline salts, phosphoric acid ester compounds, higher fatty acids, higher fatty acid ethylene oxides, or sulfone alkali salts of propylene oxide adducts, ionic dispersants, quaternary ammonia -Various dispersants are used, such as cationic dispersants such as um salt type. Being

 [0006] However, even when these dispersants are used, the conventional method of dispersing conductive particles in a resin using, for example, a disperser or a kneader sufficiently improves the dispersibility of the conductive particles. And the conductivity of the conductive paste could not be kept good.

In particular, in the case of a silver paste using silver particles as conductive particles, the true specific gravity of the silver particles is 10 Since the silver particles settled easily and the re-aggregation property was large, there was a problem that labor and time were required for the re-dispersion process for use after long-term storage. Therefore, there has been a demand for good redispersibility along with long-term storage stability.

[0007] In order to deal with such problems, for example, an attempt is made to obtain good dispersibility and stability over time by using a cationic surfactant having an organic vehicle and an alkyl group-containing sulfosuccinate. (See Patent Document 1). However, the use of the method described in Patent Document 1 is insufficient to improve the redispersibility of the settled particles. Furthermore, when the line width of the conductive circuit was narrow, it was insufficient to print the wiring pattern with high accuracy. Also, the amount of grease used for dispersion was not reduced to the minimum necessary. But it was insufficient.

[0008] On the other hand, in the production of a dispersion using metal particles, a vacuum freeze-drying method is used. For example, in the production of a tantalum powder coating material for producing an anode element for an electrolytic capacitor, tantalum powder is used. And a dispersant are mixed in a solvent and vacuum freeze-dried to adsorb the dispersant onto the surface of the tantalum particles (see Patent Document 2).

 However, there is no suggestion of the relationship between dispersibility and conductivity in the case where vacuum freeze-drying is applied to the production of conductive bases that have the same characteristics and differ greatly in required properties even with the same metal dispersion.ヽ ヽ. In addition, the selection of a dispersant for developing good conductivity is completely disclosed.

 As described above, in order to fully draw out the characteristics of the conventional polymer-type conductive paste, it is important to select an appropriate dispersing method and to select a dispersant suitable for the dispersing method. Therefore, there has been a demand for a dispersing agent and a dispersing method that realize the electrical conductivity.

[0009] In particular, in recent years, in order to reduce the electrical resistance of a conductive circuit formed from a conductive paste, the particle diameter of silver particles is extremely reduced, or particulate silver containing particulate silver oxide or tertiary fatty acid silver The use of a silver paste that can be fired at a low temperature using a composite is being studied. In this low-temperature firing type silver paste, in the case of finely divided silver particles, adjacent particles are fused together by heating at 300 ° C. or lower, and the electrical resistance of the conductive circuit is lowered. In the case of particulate silver compounds, heating up to 300 ° C or reducing agent By heating in the presence, the silver compound is reduced to become metallic silver, and adjacent silver particles are fused together to reduce the electrical resistance of the conductive circuit (see, for example, Patent Document 3).

[0010] Conventionally, polymer-type conductive pastes are made of spherical or flakes by adding a binder such as acrylic resin, epoxy resin, polyurethane resin, polyester resin, organic solvent, curing agent, catalyst, etc. The conductive particles were dispersed and mixed, and the conductivity was obtained by contact between the conductive particles due to curing shrinkage when the binder was cured. For this reason, the electrical resistance becomes relatively high, and the cohesive force of the cured resin changes due to a temperature change or the like, and accordingly, a conductive circuit or the like formed using a polymer-type conductive paste is used. The electrical resistance is likely to fluctuate and has a drawback.

[0011] The low-temperature firing type silver paste compensates for these drawbacks. By using this silver paste, a conductive circuit having good conductivity can be formed on a plastic film such as PET. can do.

 However, the finely divided submicron silver fine particles and particulate silver compounds used in low-temperature fired silver pastes are highly reactive and are difficult to handle in a dry powder state. In particular, the particulate silver compound has a very fast reduction reaction, and therefore has the power to be stored in a solution such as water or a solvent having low reducibility. In particular, when an alcohol solvent or the like is used as a dispersion solvent, reduction proceeds during dispersion of the silver paste, and fusion between silver particles may occur contrary to dispersion. For this reason, it is further required to disperse these silver and silver compound particles to primary particles to coat and stabilize the surface of each particle.

Furthermore, in order to obtain the original high electrical conductivity in these silver pastes, the silver particles in the silver paste must be well dispersed while maintaining a high silver content. It is necessary to perform the stabilization with fat, make the coating thickness on the surface of the particles as thin as possible, and make it easy to fuse adjacent particles by low-temperature firing. If the film formed on the surface of the silver and silver compound particles is too thick, adjacent particles are difficult to fuse with each other, and the filling degree of silver or silver compound is also reduced. The inherent advantages of these low-temperature fired silver pastes that give a high temperature are not exhibited. Therefore, for these low-temperature firing type silver pastes, individual silver or silvery compound It was even more important to select a dispersant and a manufacturing method that simultaneously satisfy the stability by particle coating, the improvement of dispersibility, and the improvement of conductivity by low-temperature firing.

 Patent Document 1: Japanese Patent Laid-Open No. 2000-231828

 Patent Document 2: JP 2004-006502 A

 Patent Document 3: Japanese Patent Laid-Open No. 2003-309337

 Disclosure of the invention

 Problems to be solved by the invention

[0012] An object of the present invention is to provide a conductive circuit having a good conductive property with a narrow line width in which fine particles of silver or silver-containing compound are well dispersed and there is no change over time in physical properties such as an increase in viscosity. It is to provide a silver paste that can be formed.

 A further object of the present invention is to provide a method for producing a silver-containing powder that has undergone a surface treatment that is indispensable for the production of the silver paste.

 A further object of the present invention is to provide a silver base that can be fired at a low temperature and can form a coating film having high conductivity after firing, by using particles of silver or a silver compound having a low sinterable temperature. Is to provide.

 Means for solving the problem

[0013] The present invention provides a particle force of silver or a silver compound, an alkylamine-based or alkylamine salt-based surfactant, or a phosphate ester-based surfactant having a phosphorus content of 0.5 to 10% by mass. There is provided a method for producing a surface-treated silver-containing powder characterized by having a drying step of freeze-drying a dispersion dispersed in a dispersing solvent together with an agent.

 Furthermore, the present invention provides a silver paste containing the surface-treated silver-containing powder and greaves.

 The invention's effect

 [0014] By using the method for producing a surface-treated silver-containing powder of the present invention, particles of silver or a silver compound are dispersed as fine particles, and a surfactant is present on the surface of each particle of silver or a silver compound. Adsorbed and the particle surface is well coated.

Usually, silver particles such as silver, which have a large specific gravity, are easily settled by ordinary processing methods. Since the concentration distribution is likely to occur in the disperser, it is difficult to perform a uniform treatment, but by dispersing in a solvent containing a surfactant and then performing freeze-drying in a vacuum using the method of the present invention, The surface of silver or silver composite particles can be processed under uniform processing conditions. Furthermore, in the present invention, surface treatment is performed using an alkylamine-based or alkylamine salt-based surfactant or a phosphate ester-based surfactant having a phosphorus content of 0.5 to 10% by mass. Therefore, the surfactant is very well adsorbed on the particle surfaces of silver and silver compounds, and the dispersibility is improved.

[0015] When a silver-containing powder whose surface is treated with a surfactant is used, a silver paste having a wide range of viscosities can be obtained only by mixing or stirring with a solvent or a mixture of a resin and a solvent or a simple dispersion operation. Can be made. Since the surface of the particles made of silver or silver compound is already surface-treated with a surfactant, the particles having silver or silver compound can be well dispersed in the silver paste. Moreover, the addition amount of the resin as a dispersant can be suppressed to a small amount as compared with the case where the untreated metal particles are dispersed. Further, since the amount of the resin coating on the particle surface is not increased, the conductivity when the conductive paste is formed is not reduced. Further, as a result, it is possible to improve the blending ratio of silver or silver compound particles, which is effective in improving conductivity. In addition, since silver or silver composite particles are finely dispersed in the solvent together with the binder resin, a silver paste having excellent characteristics can be produced.

 [0016] In the conventional method in which the paste viscosity is defined by the use disperser, the base viscosity after completion of the dispersion is usually readjusted to the optimum viscosity according to each printing method. For example, in order to set a high viscosity that is optimal for the screen printing method, it was sometimes necessary to reduce the amount of solvent by evaporating the solvent of the paste after dispersion.

However, if the surface treatment of silver particles as described above is performed using a surfactant such as an alkylamine-based phosphate ester, a paste is formed simply by mixing and stirring with the solvent and resin for forming the paste. be able to. As a result, it is possible to easily produce a silver paste having a silver powder content and viscosity most suitable for the printing means used for producing the conductive circuit. The silver paste of the present invention can be stored for a long period of time because it can be easily stabilized by redispersion with a stirring degree even if the standing period after the paste is produced is long. Also manufactured by the manufacturing method of the present invention It can be stored in the state of the surface-treated silver-containing powder, and only the necessary amount of silver paste can be produced as required.

 Brief Description of Drawings

 [0017] FIG. 1 is an explanatory view schematically illustrating a surface treatment method of silver powder with a surfactant according to the present invention.

 FIG. 2 is a diagram showing an example of measurement results of DSC analysis of silver powder after surface treatment according to the present invention.

 FIG. 3 is a view showing the particle size distribution of the surface-treated silver powder prepared in Example 1 and Comparative Example 1 on a volume basis.

 [FIG. 4] The resistivity of the dried coating film with the conductive paste prepared in Example 1 and Comparative Example 1

It is a figure showing the result measured by changing the calcination time in 250 ° C.

 FIG. 5 is a view showing the particle size distribution of the surface-treated silver powder prepared in Example 4 on a volume basis.

 FIG. 6 is a graph showing the particle size distribution of the silver powder after the surface treatment produced in Example 5.

 FIG. 7 is a view showing a profile of a fine line pattern produced by screen printing using the silver paste produced in Example 5.

 FIG. 8 is a graph showing the relationship between the heating time (firing time) and the volume resistivity of the fine line pattern when the fine line pattern produced with the silver paste of Example 5 was baked at 160 ° C. or 250 ° C. It is.

 Explanation of symbols

 [0018] a ... silver or silver compound powder (particles), b ... surfactant (molecule), c ... surface-treated silver-containing powder (particles)

 BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The present invention is described in further detail below. In the present invention, “sintering of silver or silver compound particles” means that a substance containing silver or silver compound particles (for example, powder or paste) is heated to produce silver or silver compound. This refers to melting and fusing particles of a product. In addition, “baking of silver paste” refers to a portion in which adjacent silver or silver compound particles are brought into contact with each other or are brought into contact with each other by heating the silver paste to cure and shrink the contained resin. It refers to fusing the minutes. “Dispersion” refers to a phenomenon in which other phases are dispersed in the form of fine particles in a continuous phase.

 [0020] By using a silver-containing powder obtained by surface-treating silver or silver compound particles according to the present invention, a silver paste having excellent dispersibility and good conductivity can be produced. In particular, particles of silver or silver compounds having a low sintering temperature, such as ultrafine fine particles of silver or silver compounds, silver or silver compounds having low crystallinity (small crystallite diameter) When silver oxide-treated silver particles are applied, it can be fired at a much lower temperature (lower firing temperature) than conventional high-temperature firing type conductive paste, and has good conductivity after firing. The silver paste which can form the wiring pattern which has can be obtained.

 [0021] As the silver particles used in the present invention, pure silver particles, metal particles surface-coated with silver, or a mixture thereof can be used. As the silver particles, particles having an arbitrary shape such as a spherical shape, a scale shape, a needle shape, or a dendritic shape can be used. The method for producing silver particles is not particularly limited, and may be any method such as a mechanical pulverization method, a reduction method, an electrolysis method, or a gas phase method. The metal particle surface-coated with silver is obtained by forming a silver coating layer on the surface of a particle having a metal force other than silver by a method such as plating. For example, the surface of copper particles coated with silver is commercially available. As the silver particles, spherical silver particles and scaly silver particles made of only silver are preferred in view of conductivity and cost.

 The volume average particle diameter of the spherical silver particles is preferably 0.05 to 10 / ζ πι, more preferably about 0.05 to 5 μm. In the case of flaky silver particles, the major axis of the flaky surface is preferably in the range of 0.05-100 μm.

 As the silver particles, combine two or more types of particles with different volume average particle diameters to improve the packing density of the silver particles, thereby improving the conductivity of the conductive film.

[0022] As silver composite particles, silver oxide, particles of silver-containing organic compounds such as aliphatic carboxylic acid silver, alicyclic carboxylic acid silver, aromatic carboxylic acid silver and the like can be used. . As these silver compound particles (particulate silver compound), those produced industrially can be used, and those obtained by a reaction from an aqueous solution containing a silver compound may be used. In particular, the use of silver compound particles having an average particle size of 0.5 m or less is preferable because the reduction reaction rate is increased. Yes. Silver compound particles having an average particle size of 0.5 m or less are produced by the reaction of a silver compound with another compound, for example, an aqueous alkaline solution such as sodium hydroxide or sodium hydroxide is added dropwise to an aqueous silver nitrate solution with stirring. It can be produced by a method of reacting to obtain acid silver particles.

 [0023] In the production method of the present invention, when a silver paste is produced, particles of silver or a silver compound capable of setting the firing temperature at which the silver particles are fused by heating the silver paste to 300 ° C or less. Is preferred to use. With such a low firing temperature and a low-temperature firing type silver paste, for example, a wiring pattern formed on a polyimide film or a PET film can be fired as it is. In general, the more finely conductive particles are dispersed in the conductive paste, the lower the heat capacity of the conductive paste and the firing temperature of the conductive paste becomes the intrinsic sintering temperature of the conductive particles themselves. Get closer. Furthermore, since the packing density improves as the conductive particles are finely dispersed, generally the higher the dispersion, the better the conductivity after firing.

 [0024] Moreover, the silver paste using the surface-treated silver-containing powder by the production method of the present invention can reduce the resin component, and the film thickness of the resin covering the particles of silver or silver compounds can be reduced. Since it is thin, adjacent silver or silver composite particles are easily fused after firing. For this reason, low-temperature sintering type silver or silver compound particles having a sintering temperature of 300 ° C or less are used as silver or silver compound particles subjected to surface treatment with a surfactant. If used, a low temperature firing type silver paste can be obtained even after the surface treatment with a surfactant, and the low temperature sintering type silver paste can be obtained sufficiently. A favorable wiring pattern can be obtained.

[0025] As the silver particles having a low sintering temperature, silver particles having a volume average particle diameter of 0.05 to 10 m can be used. It is preferable that the silver particles have a volume average particle diameter of 0.05 to 5 / ζ πι. In the surface treatment method according to the present invention, when silver particles or silver compound particles are produced in a liquid phase, these particles having a small volume average particle size and high activity can be effectively surface-treated. In addition, the silver or silver compound particles can be surface-treated in the presence of a surfactant while being dispersed in the liquid phase when the particles are produced. Therefore, it is easy to process, and the original characteristics of these particles with low sintering temperature are sufficient. Can be demonstrated. Examples of methods for producing silver fine particles include gas evaporation (JP-A-3-34211) and reduction precipitation using an amine compound for reduction (JP-A-11-319538).

 [0026] Furthermore, silver particles having a low crystallinity can be used as the silver particles having a low sintering temperature. When the crystallinity of silver particles is low, the crystallite size is usually small. Therefore, by reducing the crystallite diameter, the fusion temperature (sintering temperature) between silver particles can be remarkably lowered. In order to lower the firing temperature of the silver paste to 300 ° C. or lower, the crystallite diameter is preferably 0.1 to 20 nm, more preferably 0.1 to LOnm.

 [0027] Also, the sintering temperature is low! As the silver or silver compound particles, silver particles in which some of the particles have been subjected to acid-silver treatment can be used. In addition to the method of oxidizing the surface of the silver particle from silver to silver oxide by partially oxidizing the surface of the silver particle, the silver oxide-treated silver particle has a layer of oxidized silver on the surface of the silver particle. It can be obtained by a method of forming a coating.

 [0028] By the oxidation treatment of the silver particle surface, the silver on the particle surface is oxidized into first silver oxide, second silver oxide, and the like. In the silver particle whose surface is coated with acid silver, the silver oxide on the surface of the particle may be in a mixed state of first silver oxide, second silver oxide, and the like. In these silver particles whose surface is coated with silver oxide, the silver oxide on the surface layer becomes silver by a reduction reaction in the absence of a reducing agent or in the presence of a reducing agent, and adjacent particles are fused at a low temperature. Silver particles having a surface subjected to silver oxide treatment can be appropriately selected from those having different compositions and shapes according to the reduction reaction conditions; heating temperature, presence / absence of a reducing agent, reducing power of the reducing agent, and the like. The silver oxide-treated silver particles have a volume average particle size of preferably about 0.05 to 10 111, more preferably about 0.05 to 5 / ζ πι. In particular, the use of particles having an average particle diameter of 0.05 to 0.5 m is preferable because the reduction reaction rate is increased.

[0029] When silver particles surface-treated with silver oxide are used, the organic matter around the particles is oxidized by the oxygen released during the reduction to acid-silver power, and heat is generated. The effect of lowering the apparent firing temperature of the silver paste is obtained. Therefore, the silver oxide content of silver particles surface-treated with silver oxide is preferably 1% by mass or more (silver content 99% or less), and the silver oxide content is 5% or more (silver content 95% by mass). % Or less) is particularly preferred. Further, from the viewpoint of facilitating the fusion of silver particles, it is necessary to have a certain amount of metallic silver inside the particles. The preferred silver oxide content is 30% by mass or less (silver content is 70% by mass or more), and the preferred silver oxide content is 20% by mass or less (silver content 80% by mass or more). A preferable range of the silver oxide content of the silver particles surface-treated with silver oxide is 1 to 30% by mass, and a more preferable range is 5 to 20% by mass.

 [0030] By applying a surface treatment method characterized by vacuum freeze-drying, which is effective in the present invention, to these acid-silver-silver-treated silver particles, the firing temperature having good conductivity and low temperature is achieved. In addition to being able to produce a silver paste, these particles, which are very easy to reduce when dried, can be stored stably. In addition, since silver particles are stably dispersed as fine particles (primary particles) even in the silver paste, it is possible to prevent unnecessary agglomerates from being generated due to the fusion of particles during reduction, and in fine printing. There is no problem.

 [0031] (Surfactant)

 In the present invention, as the surfactant used for the surface treatment of silver or silver composite particles, an alkylamine-based or alkylamine salt-based surfactant, and a phosphorus content of 0.5-: LO Examples thereof include phosphate ester-based surfactants having a mass%.

 [0032] (Surfactant of alkylamine and alkylamine salt)

 As the surfactant used in the present invention, alkylamines and alkylamine salts can be suitably used. Alkylamine-based nonionic surfactants and alkylamine salt-based cationic surfactants are effective even when used alone. Especially when used in combination, the dispersibility becomes better and the effect is remarkable. is there.

 As the alkylamine-based surfactant, a polyoxyethylenealkylamine-type surfactant is more preferred, and a polyoxyalkylenealkylamine-type surfactant is more preferred. Of these, those having the following general formula (1) are more preferred.

[0033] [Chemical 1]

[0034] (a and b are each an integer of 1 to 20, and R represents an alkyl or alkylaryl group having 8 to 20 carbon atoms.) On the other hand, alkylamine salt surfactants are preferably alkylamine acetates, more preferably those having the following general formula (2).

[0035] [Chemical 2]

(R- NH ₃ ⁺ XCH ₃ CO〇-) (2)

(R represents an alkyl group having 8 to 20 carbon atoms or an alkylaryl group.)

 [0037] In the general formula (1) and the general formula (2), the alkyl group having 8 to 20 carbon atoms may be a linear alkyl group or a branched alkyl group, for example, an octyl group, a nonyl group, a decyl group, Examples include undecyl, dodecyl, lauryl, tetradecyl, myristyl, hexadecyl, cetyl, octadecyl, stearyl, and eicosyl groups. Examples of the alkylaryl group having 8 to 20 carbon atoms include alkylfuryl groups such as octylphenyl group, nourphehl group and dodecylphenyl group. The alkyl part of the alkylaryl group may be a straight chain alkyl group or a branched alkyl group! /.

 [0038] When the alkylamine surfactant and the alkylamine salt-based cationic surfactant are used alone or in combination, the total amount of the surfactant with respect to the silver or silver compound particles is as follows: It is necessary to adjust appropriately depending on the type of particles of silver or silver compound, but, for example, 0.01 to 3,000 parts by mass is preferable with respect to 100 parts by mass of silver or silver compound particles. 05-: L is more preferably 50 parts by mass. When the total amount of the surfactant is 0.01 parts by mass or more, sufficient dispersibility tends to be easily obtained. On the other hand, if the amount is less than 3.00 parts by mass, the surface of the silver or silver compound particles is thinly coated with the organic component of the surfactant, making it easy to obtain contact between the particles after drying. Tend to improve.

 When an alkylamine surfactant and an alkylamine salt-based cationic surfactant are used in combination, the mixing ratio of the alkylamine salt to the alkylamine salt salt is in the range of 1:20 to 1: 5. preferable.

 [0039] (Phosphate-based surfactant)

The phosphate ester-based surfactant used in the present invention is a surfactant mainly composed of phosphate monoester or phosphate diester, and has a phosphorus content of 0.5 to 10 mass. % Is used. Phosphate ester surfactants are polyoxyalkylene The following general formula (3) which is preferably a phosphoric ester of rualkyl ether

[0040] [Chemical 3]

[R- 0- (G ₂ H ₄ 0) _n ] ₃ — P = 0

 I (3)

(0H) _X

[0041] (in the general formula (3), R represents an alkyl or alkylaryl group having 1 to 20 carbon atoms, n is an integer of 1 to 20, and X is an integer of 1 or 2) It is even more preferable to have

 [0042] In the formula (3), the alkyl group having 1 to 20 carbon atoms may be a linear alkyl group or a branched alkyl group, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group. Group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, lauryl group, tetradecyl group, myristyl group, hexadecyl group, cetyl group, octadecyl group, stearyl group And eicosyl group. Examples of the alkylaryl group having 20 or less carbon atoms include alkylfuryl groups such as octylphenyl group, nourphehl group, dodecylphenol group and the like. The alkyl part of the alkylaryl group may be a straight chain alkyl group or a branched alkyl group! /.

 [0043] It is preferable that the carbon number of R is 1 to 10, n is 1 to 10, and the sum of the carbon number of R and n is 7 to 15. The weight average molecular weight of the phosphate ester surfactant is preferably from 100 to 10,000, and more preferably from 150 to 5,000. The content of P (phosphorus) is preferably 0.5 to 10% by mass, more preferably 1 to 7% by mass, and particularly preferably 2 to 6% by mass. More preferably, it is 2 to 5% by mass.

 Further, as the phosphate ester surfactant used in the production method of the present invention, the ability to use HLB (hy drophile-lipophile balance) of 10 or more, or adding a basic compound to neutralize the acid value. It is preferable to use it.

[0044] The type and blending amount of the phosphate ester-based surfactant can be appropriately selected depending on the type of silver or silver compound particles. The amount of the phosphate ester-based surfactant needs to be adjusted as appropriate depending on the type of silver or silver compound particles. 01 to 3,000 mass repulsive force S is preferable, and 0.05 to 0.50 mass repulsive force is more preferable. If the surfactant is 0.01 parts by mass or more, sufficient dispersibility is easily obtained. Tend. On the other hand, at less than 3.00 parts by mass, the surface of the silver or silver compound particles is thinly coated with the organic component of the surfactant, making it easier to obtain contact between the particles after drying, and the conductivity tends to be improved. .

 [0045] (1) Dispersion preparation process

 In the method for producing a surface-treated silver-containing powder of the present invention, first, silver or silver compound particles have an alkylamine-based or alkylamine salt-based surfactant or a phosphorus content of 0.5-10. A dispersion liquid is prepared which is dispersed in a dispersion solvent together with a phosphate ester-based surfactant having a mass%.

 [0046] (Solvent for dispersion)

 Here, the dispersion solvent (dispersion medium) used for dispersing the silver or silver compound particles is not particularly limited as long as it is suitable for dissolving the surfactant. For example, water; And lower alcohols such as isopropyl alcohol; propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ethers and the like with ethylene alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether. Of these dispersing solvents, water is preferred.

 These dispersing solvents are not limited to those listed here, but can be used alone or in admixture of two or more (for example, as an aqueous solution or a mixed solvent).

[0047] (Method for preparing dispersion)

As a method of preparing a dispersion liquid in which silver or silver compound particles are dispersed together with the surfactant, silver or silver compound particles and a surfactant are added to a dispersion solvent, and the mixture is stirred. And a method of crushing the particles of silver or silver-containing compound into fine particles (primary particles) and mixing with the surfactant using a machine or a dispersing machine. In this case, for example, silver particles, a dispersion solvent, and a surfactant are mixed at a desired ratio, and the silver particles are pulverized into primary particles by a disperser or the like and dispersed in the dispersion solvent. Thus, a dispersion of silver particles can be obtained. The same applies when silver compound particles or silver oxide-treated silver particles are used instead of silver particles. Silver or silver used as a raw material when added to the solvent for dispersion If the compound particles are silver or silver compound powder (dry powder), it is easy to optimize the amount of particles such as silver, and it is possible to prevent mixing of undesired ingredients in the dispersion process. There are advantages and favors.

 Usable stirrers or dispersers can be appropriately selected from the known stirrers or dispersers described below.

[0048] When the silver or silver compound powder is dispersed in a dispersion solvent, a surfactant or the like may be added to the dispersion solvent and sufficiently dissolved, and then the silver or silver compound powder may be added. preferable. If necessary, the solubility of the surfactant in the dispersion solvent can be increased by neutralization of the surfactant (for example, in the case of a phosphate ester surfactant, formation of a phosphate ester salt with an alkali or the like). it can. When dispersed for 0.5 to 4.0 hours after compounding, secondary particles (aggregated particles) in the silver powder or silver composite powder are crushed into primary particles, and the surfactant and silver or silver Adsorption equilibrium with the primary particles of the compound.

[0049] Another method for preparing a dispersion is to synthesize silver or silver composite particles (hereinafter sometimes referred to as "silver particles") in a liquid phase, and then use a mother liquor. Force Filter silver particles, etc., wash the silver particles, and disperse them in the solvent for dispersion. In this method, it is desirable not to dry particles such as silver, and the presence or absence of a treatment such as filtration or washing can be appropriately set. In addition, a mother liquor solvent (for example, water) obtained by synthesizing particles such as silver can be used as a dispersion solvent in the dispersion as it is. In this case, the process of separating particles such as silver by mother liquid filtration can be omitted. If unnecessary components coexist in the mother liquor, the unnecessary components are removed as necessary. Then, a necessary amount of a surfactant is added to the dispersion liquid in which particles such as silver are dispersed, and then subjected to lyophilization treatment. If a suitable surfactant has already been added to the mother liquor, it can be used for lyophilization treatment, or a surfactant may be added.

According to this method, since particles such as silver produced in the liquid phase are primary particles, it is possible to obtain a dispersion liquid in which particles such as silver are dispersed together with a surfactant while suppressing aggregation of particles such as silver. Can do. In this case, it is not necessary to use a stirrer or a disperser to disintegrate secondary particles such as silver into primary particles. Can be dispersed as a primary particle in a solvent for dispersion to achieve a desirable dispersion state. wear.

 [0050] The dispersion of particles of silver or the like containing a surfactant produced by the dispersion production method exemplified above is subjected to freeze-drying in the next step. The range of the solid content concentration in the dispersion liquid of particles such as silver when freeze-drying is preferably 0.5 to 80% by mass, particularly preferably 1 to 50% by mass.

 [0051] In the present invention, when a phosphate ester-based surfactant is used, it is preferable that the dispersion liquid has an acidic condition (for example, ρΗ1 to 3) as a result of use, and an alkylamine or alkylamine salt-based interface is preferred. When an activator is used, it is preferable that the dispersion is in an alkaline condition (for example, pH 12-14). As a result, an interfacial electric double layer is formed on the surface of particles such as silver via the surfactant, and dispersion stability is obtained. In addition, in the phosphate ester system and the alkylamine or alkylamine salt system, since the charge when the hydrophilic group portion is ionized is opposite, depending on the sign of the surface charge of the particle such as silver, the particle It is preferable to select a surfactant so that repulsive force works.

 [0052] For example, in the case of silver particles having a surface treated with silver oxide, an alkylamine or an alkylamine salt-based surfactant is preferred. There is a feature that is large. In addition, in the case of pure silver particles (silver particles whose surface is not treated with silver oxide), phosphoric acid ester-based surfactants are preferred. It has the feature of being excellent.

 [0053] (2) Drying process

 After the particles of silver or silver compound are sufficiently dispersed in the dispersion solvent in the presence of a surfactant, the dispersion solvent is removed from the dispersion by a vacuum freeze-drying method.

 In the production method of the present invention, since vacuum freeze-drying is used as a drying method, it is preferable to select and use a solvent that is easily frozen from the power of the solvent. Considering that the cooling capacity of generally available equipment is up to about 40 ° C for vacuum freeze-drying, select a dispersion solvent with a freezing point of 40 ° C or higher. This is preferable because the implementation cost can be reduced.

[0054] In the vacuum freeze-drying method used in the production method of the present invention, basically a low temperature Only the dispersion solvent is sublimated and removed from the dispersion frozen in the state. In this process, the surfactant is not eluted and lost in the dispersion solvent, so almost all of the added surfactant remains in the silver or silver compound powder after the treatment. As shown in Fig. 1, surfactant b is localized in the vicinity of the surface of silver or silver composite particles a in the dispersion, and vacuum lyophilization is performed to remove only the solvent for dispersion. Sometimes the surfactant b is likely to be removed while adsorbed uniformly on the surface of the silver or silver composite particles a. It can be said that it is an extremely efficient treatment method in which the particles a of silver or silver compound and the surface-treated particles c do not aggregate at the time of removal as in the case of removal. In this way, all the surfactant b used in the dispersion remained on the surface of the silver or silver composite particle a even after vacuum freeze-drying, and was surface-treated with the surfactant b. Since the particles c of silver or silver compound are provided in a high yield, it is easy to grasp the relationship between the effect of the surfactant and the amount used. In addition, it is easy to optimize the amount used, so it is possible to prevent an excessive amount of surfactant from being added.

 Since the molecule of the surfactant b is adsorbed on the surface of the silver or silver compound particle a at the end of the hydrophilic group, the end of the hydrophobic group faces the outside of the particle. This improves the affinity with the binder resin and improves the dispersibility of the surface-treated silver or silver compound particles c. Further, aggregation between particles can be suppressed, and the state of being dispersed in primary particles can be maintained. Freeze-vacuum drying is performed by, for example, pre-freezing the dispersion liquid below the freezing point of the dispersing solvent at atmospheric pressure. Furthermore, it is possible to use a method in which the degree of vacuum is controlled at a pressure lower than the vapor pressure of the solvent for dispersion at the freezing point, and theoretically, the molecules of the solvent for dispersion are removed from the solid mixture in the frozen state. Can be sublimated.

For example, in the case of a dispersion using water as a dispersion solvent (a dispersion containing silver or silver compound particles, water, and a surfactant), prefreeze to 0 ° C or lower at atmospheric pressure. Theoretically, the degree of vacuum should be controlled so that the vapor pressure of water at 0 ° C does not exceed 4.5 mmHg (= 600 Pa)! Considering the drying speed and ease of control, it is preferable to increase the temperature to the melting point (freezing point) at the vapor pressure below lmmHg (= 133.32 Pa). Thus, in the drying method by vacuum freeze-drying, the solvent for dispersion is sublimated and evaporated in vacuum to dry the particles, so that the shrinkage due to drying is slight, and the structure and structure are not easily destroyed. In addition, as in hot air drying, low-temperature drying is performed in a frozen state of a solid that does not move due to drying of liquid components such as water in the sample at high temperatures, so partial component concentration, partial component change, deformation There is almost no preferable.

 [0056] (3) Production of silver paste

 In order to produce a conductive paste (silver paste) using the surface-treated silver-containing powder produced by the production method of the present invention, the surface-treated silver-containing powder (silver or silver compound powder) is used. Then, a solvent or binder resin and a solvent are mixed, and silver or a silver compound powder is dispersed using an appropriate dispersing machine.

 [0057] Solvents used in the production of the silver paste of the present invention are alcohols such as methanol, ethanol, n-propanol, benzyl alcohol, terpineol (Terpineol); acetone, methyl ethyl ketone, cyclohexanone, isophorone, Ketones such as cetylacetone; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Ethers such as tetrahydrofuran, dioxane, methylcelesolve, diglyme and butylcarbitol; Acetic acid Esters such as methyl, ethyl acetate, jetyl carbonate, quinone (1-isopropyl-2,2-dimethyltrimethylenediisobutyrate), carbitol acetate, butyl carbitol acetate; sulfoxides and sulfones such as dimethyl sulfoxide, sulfolane; Methylene chloride, black mouth form, tetrasalt Carbon, aliphatic halogenated hydrocarbons such as 1,1,2-trichloroethane; aromatics such as benzene, toluene, o-xylene, p-xylene, m-xylene, monochrome benzene, dichlorobenzene, etc. It is done.

 These solvents are not limited to those listed here, but can be used alone or in admixture of two or more.

 [0058] The silver or silver compound powder surface-treated by the method of the present invention may be used as a silver paste applied on a substrate in a state of being dispersed in the solvent, but further binding. It is preferable to add an agent resin to improve the dispersion stability of the silver or silver compound, and to improve the adhesion to the substrate and use it as a silver paste.

[0059] Examples of the binder resin that can be used in the silver paste of the present invention include acrylic resin and petital resin. Fatty, Polybulal Alcohol, Acetal, Phenolic, Urea Resin, Bellemardiacetate, Polyurethane, Polyester, Polyacetate, Epoxy, Melamine, Alkyd It is possible to use cocoa butter, nitrocellulose cocoa and natural rosin alone or in combination of two or more.

[0060] The amount of binder resin used is preferably in the range of 0.01 to 30 parts by mass per 100 parts by mass of the surface-treated silver-containing powder, and particularly preferably in the range of 0.01 to 10 parts by mass. .

 The amount of solvent used varies depending on the coating method and printing method, and the amount used may be selected as appropriate.

 [0061] If the surface-treated silver-containing powder of the present invention is used as a raw material, a simple dispersion treatment such as stirring is performed using a solvent or a solvent and a binder resin when a silver paste is required. Only then can the silver paste be produced quickly. In other words, a good silver paste can be obtained by performing a simple stirring operation of the additive solvent or the additive solvent and the additive binder immediately before printing. Do not need. However, in order to perform the dispersion more reliably, the dispersion process may be performed using the following dispersion means.

 [0062] Examples of dispersing means that can be used include two rolls, three rolls, a ball mill, a sand mill, a pebble mill, a tron mill, a sand grinder, a seg barrier striker, a high speed inverter disperser, a high speed stone mill, Examples thereof include a high-speed impact mill, an adader, a homogenizer, and an ultrasonic disperser. By using these, kneading and dispersing can be performed.

 [0063] The silver paste, which has been kneaded and dispersed, is generally printed as a paste-like composition on an insulating film or an insulating substrate by a commonly known application method or printing method, and this is heated. A conductive circuit can be formed.

The silver paste of the present invention can form a coating by various coating methods. For example, known roll coating methods, such as air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnated coat, river slow coat coat, transfer roll coat coat, The coated product can be formed on the substrate by gravure coating, kiss coating, cast coating, spray coating or the like. Various printing methods can also be applied. The printing method also has an optimum viscosity area as in intaglio printing. There are those in a relatively low viscosity region and those in a high viscosity region such as screen printing. Specifically, the coating material can be printed in a predetermined size on the substrate using a stencil printing method, an intaglio printing method, a lithographic printing method, or the like.

 [0064] Examples of the material of the substrate during coating or printing include polyethylene terephthalate film (PET film), polyimide film (PI film), and green sheet (inorganic substrate). Silver paste may be printed on these films in a predetermined pattern, and the printed material may be dried and then heat-cured.

 The thickness of the printed material varies depending on the printing method. The thickness of the printed material is preferably in the range of 1 to 30 m, particularly preferably 1 to 15 m. In order to increase the electric resistance (volume resistance) per unit volume after the printed material is dried, the substrate may be pressed or calendered to such an extent that the substrate is not markedly deformed.

 [0065] The coated material thus obtained is dried at, for example, about 160 ° C for about 5 minutes, and then the binder resin is cured by a heat treatment step of about 250 ° C. Thereby, conductive circuits for various electronic circuit boards are obtained.

 In particular, when silver oxide fine particles or silver particles whose surface is treated with silver oxide are used as particles of silver or a silver compound, the heat treatment reduces the silver oxide to silver as it is cured and is released along with the reduction reaction. Oxygen can be used to oxidize the surrounding surfactant and rosin, and generate heat. As a result, the silver particles in which the silver oxide has been reduced can be fused by a heat treatment at a lower temperature (for example, 160 to 200 ° C.) than when pure silver particles are used. Therefore, silver paste using acid silver particles or silver particles treated with acid silver can reduce the requirement for heat resistance of the substrate material during coating or printing, so PET, PI, and others It is particularly suitable for a substrate having a force such as plastic.

[0066] Fig. 2 shows a silver powder after surface treatment with a surfactant prepared using silver powder that is sintered at low temperature (silver powder with a small crystallite diameter), and silver powder that is subjected to silver oxide treatment at low temperature (silver oxide treatment). The results of differential thermal analysis (DSC analysis) of the silver powder after surface treatment with a surfactant prepared using a small crystallite diameter silver powder) are shown.

As a result of DSC analysis of the silver powder after the surface treatment of the present invention produced using silver powder having a small crystallite diameter (shown by a broken line in FIG. 2), an endothermic peak indicating melting of the silver powder is present at 215 ° C. It was. This means that the silver powder has a small crystallite size and therefore melts at a lower temperature than before.

 The results of DSC analysis of the silver powder after the surface treatment of the present invention produced using silver oxide-treated silver powder (shown by a solid line in FIG. 2) show an endothermic peak indicating melting of the silver powder of 215 ° C. And an exothermic peak at 134 ° C. This exothermic peak is considered to be because the silver oxide of the silver powder was decomposed and oxygen was released, and the carbon component of the surface surfactant was oxidized and a heat generation reaction occurred.

 As is clear from the above results, according to the silver powder after the surface treatment of the present invention, it is possible to produce a silver paste that can be fired at a temperature lower than before.

 Example

 [0067] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the scope of these examples. In addition, the measuring methods, such as a physical property, are as follows.

(1) Film thickness: The film thickness was measured using a film thickness meter K402B (manufactured by Anritsu).

 (2) Volume resistivity: Volume resistivity was measured with a low resistivity meter Lorester EP (manufactured by Mitsubishi Chemical Corporation) using a four-terminal measurement method. The volume resistivity was determined from the film thickness of the conductive film of the test piece. The volume resistivity was expressed by, for example, a method of describing 8.8 × 10−6 Ω′cm as “8.8E−06 Ω′cm”.

 [0068] Further, the surfactants A and B used in this example are as follows.

 (Surfactant

 Using a surfactant Disperbyk-111 (produced by Big Chemie Co., Ltd.) having a phosphoric acid monoester having a P (phosphorus) content value of 2.7 mass% as a main component and a weight average molecular weight of 2800, The surfactant was neutralized with potassium hydroxide in such an amount that the acid component was completely neutralized to prepare a 10% by mass surfactant aqueous solution.

 (Surfactant

A surfactant having a P (phosphorus) content value of 4.4 mass% and having a weight average molecular weight of 1750 and HLB of 12 is used. Was neutralized with potassium hydroxide in such an amount that the acid component was completely neutralized to prepare a 10% by mass aqueous surfactant solution. (Surfactant c)

10 Weight _^0/0 aqueous solution 5g of coconut § Min acetate as cationic surfactants alkylamine salt, a 10 wt% aqueous solution of polyoxyethylene coconut § Le kills amine ether as surfactant Arukiruamin 0. A mixture of 5 g was used.

[0069] (Example 1)

 50 g of silver powder FHD (crystallite diameter 10 nm) manufactured by Mitsui Kinzoku Co., Ltd. with a center particle size of 0.3 μm, 2.5 g of a 10% by weight aqueous solution of surfactant A as a surfactant, and 50 g of water as a solvent And 400 g of 2 mm diameter zirconia beads were placed in a 250 cc plastic bottle, mixed, and kneaded for 4 hours using a rotating machine (ball mill) to obtain a silver powder dispersion (al).

[0070] This silver powder dispersion (al) was transferred to a flat tray having a bottom dimension of 200 mmL x 150 mmW, pre-lyophilized, and then freeze-dried. As a freeze vacuum dryer, “DFM-05AS” manufactured by Nippon Vacuum Co., Ltd. was used. Pre-frozen silver powder dispersion (al) is placed on a shelf that has been cooled to about 40 ° C in advance, and the degree of vacuum is 7 ~: After freeze-drying for 20 hours at LOPa, the surface of the silver powder as a bulky sponge-like dried product 50 g of a processed product (bl) was obtained. The particle size distribution of the silver particles at this time is shown in Fig. 3 on a volume basis. The volume average particle size was 0.6 m. Next, surface treatment product of silver powder (bl) 50g, acrylic resin "# 15-78" (manufactured by Toei Kasei Co., Ltd.) as binder resin, 5.6g (solid content = 2.5g), and carbon acetate 2.7 g of tall was placed in a 250 cc plastic bottle, mixed, and stirred for 0.5 hour using a shaker (paint conditioner) to obtain silver paste B-1. The silver paste was stable without causing viscosity increase or aggregation with time. With this paste B-1, a 50 mm x 80 mm size printing pattern was formed on the PI film with a line width of 50 m to obtain a screen-printed coating film with a thickness of 10 m. The printed coating was dried at 150 ° C for 5 minutes. After that, it was baked in an oven at 160 ° C and 250 ° C for 60 minutes, and when the state of printing was observed with a microscope, a good conductive circuit pattern without defects was formed. Further, a solid print having a thickness of 50 m was printed, and the volume resistance of the dried coating film after drying and firing was measured in the same manner.

After drying, the volume resistances after placing in an oven at 160 ° C and 250 ° C for 60 minutes showed 2.9Ε-03 Ω'cm and 6.7E-06Ω'cm, respectively. In addition, the volume resistance of the dried coating film in the oven decreased with time. Volume resistance when the oven temperature is 250 ° C Figure 4 shows the decrease.

[0071] (Example 2)

 Except that the surfactant in Example 1 was changed to Surfactant B, 105 g of the silver powder dispersion (a2) and 50 g of the surface treated product of silver powder (b2) were obtained in the same manner as in Example 1. It was. The average volume particle size of this surface-treated product was 0. The same particle size distribution as in Example 1 was exhibited. Next, 58.3 g of silver paste B-2 was obtained in the same manner as in Example 1. The silver paste was stable without causing viscosity increase or aggregation with time. A printed film was obtained in the same manner as in Example 1 by screen printing using a mask film on which a printed pattern of a conductive circuit having a line width of 50 m was formed. Furthermore, as in Example 1, solid printing with a film thickness of 50 m was performed, and after drying, the volume resistance after placing in an oven at 160 ° C and 250 ° C for 60 minutes was measured. 02 Ω 'cm and 1.5E—05 Ω' cm.

[Example 3]

 In the same manner as in Example 2, except that the silver powder FHD in Example 2 was changed to silver powder AgC-G manufactured by Fukuda Metal Foil Powder Co., Ltd. 105 g of the silver powder dispersion (a3) and the surface treatment of the silver powder 50 g of product (b3) was obtained. The volume average particle size of the silver particles at this time was 0.2 m, indicating a narrow particle size distribution.

 Next, 58.3 g of silver paste B-3 was obtained in the same manner as in Example 1. The silver paste was stable without causing a viscosity increase or aggregation with time. A printed film was obtained by screen printing using a mask film on which a printing pattern was formed in the same manner as in Example 1. Further, as in Example 1, solid printing with a film thickness of 50 m was performed, and after drying, the volume resistance after placing in a 160 ° C and 250 ° C oven for 60 minutes was measured. 5E—05 Ω 'cm, 2. 5E—05 Ω' cm.

[0073] (Example 4)

 The silver powder FHD in Example 2 was changed to silver powder Ag O'FHD whose surface was treated with 10% acid silver.

 2

In the same manner as in Example 2, 105 g of a silver oxide-treated silver powder dispersion (a4) and 50 g of a silver oxide-treated silver powder surface-treated product (b4) were obtained in the same manner as in Example 2. The particle size distribution of the silver particles at this time is shown in Fig. 5 on a volume basis. The volume average particle size was 0.7 m, indicating a narrow particle size distribution. Next, 58.3 g of silver paste B-4 was obtained in the same manner as in Example 1. The silver paste was stable without causing a viscosity increase over time. A printed film was obtained by screen printing using a mask film in which a printed pattern was formed in the same manner as in Example 1. Further, a solid printing with a film thickness of 50 m was carried out in the same manner as in Example 1, and the printed coating film was dried at 150 ° C. for 5 minutes. Thereafter, the volume resistance of the dried coating film in an oven at 160 ° C. and 250 ° C. was measured. After drying, the volume resistance after placing in an oven at 160 ° C and 250 ° C for 60 minutes showed 9.8 cm—05 Ω'cm and 1.5E—05 Ω'cm, respectively.

[Example 5]

50 g of 10% silver oxide-treated silver powder FHD (crystallite size lOnm) manufactured by Mitsui Kinzoku Co., Ltd. with a center particle size of 0.3 μm, surfactant C (copolymer as a cationic surfactant of alkylamine salt) co 10 mass nut § Min acetate _^0/0 aqueous solution of 5 g, 0. 5 g of 10 wt% aqueous solution of polyoxyethylene coconut alkyl amine ether as a surfactant Arukiruamin), water 50g which is a solvent, and 2mm diameter 400 g of Zirco Your beads were mixed in a 250 cc plastic bottle, and kneaded for 4 hours using a rotating machine (ball mill) to obtain a silver paste (a5).

 [0075] 100g of this silver powder dispersion (a5) was transferred to a flat tray having a bottom dimension of 200mmL x 150mmW, pre-lyophilized, and then freeze-dried. As a freeze vacuum dryer, “DFM-05AS” manufactured by Nippon Vacuum Co., Ltd. was used. Place the pre-frozen silver powder dispersion (a5) on a shelf that has been cooled to about 40 ° C in advance, and then vacuum degree 7 ~: Freeze-vacuum drying for 20 hours at LOPa. 50 g of treated product (b5) was obtained. Figure 6 shows the particle size distribution of the surface-treated silver particles.

[0076] Next, 50 g of a silver powder surface-treated product (b5), “Barnock DE-140-70” (manufactured by Dainippon Ink & Chemicals, Inc.) and “Barnock DB980” (Dainippon Ink & Chemicals ( Binder Knob Fatty Acid, which is obtained by replacing the solvent component of “Bernock DB980K” (manufactured by Dainippon Ink & Chemicals, Inc.) with carbitol acetate as an isocyanurate prepolymer component. = 2.5 g), and 4.2 g of carbitol acetate are mixed in a 250 cc plastic bottle and mixed with a shaker (paint conditioner) for 0.5 hours to obtain silver paste B-5. It was. This silver paste B-5 is formed on a PI film to form a 50mm x 80mm rectangle and a printed pattern of LineZSpace = 40μm / 40μm. A screen printed coating was obtained. The average thickness of the rectangular printed film was 12 m. On the other hand, the thickness distribution in the printed pattern was measured with a laser microscope (VK-9500 Keyence). The profile is shown in Figure 7. Here, the specifications of the screen plate are 640 mesh, wire diameter 15 m, calendar thickness 22 μm, emulsion thickness 10 μm. The average peak height of the printed pattern was 11.9 m.

 [0077] The rectangular printed coating film was dried at 150 ° C for 5 minutes. After drying, the volume resistivity after being placed in an oven at 160 ° C and 250 ° C for 60 minutes showed 3.7Ε-05Ωcm and 7.5E-06Ω'cm, respectively. . In the oven, the volume resistivity of the dried coating decreases with time. Figure 8 shows the decrease in volume resistivity when the oven temperature is 160 ° C and 250 ° C.

 [0078] (Comparative Example 1)

 Instead of the surfactant in Example 1, an acrylic surfactant having a weight average molecular weight of 2500 having a phosphoric acid diester having a P content value of 0.4 mass% as a component Disperbyk— 2 001 (Bic Chemie Corp.) (Manufactured) In the same manner as in Example 1 except that 0.5 g was used, 105 g of a silver powder dispersion (a6) and 50 g of a surface-treated silver powder (b6) were obtained. The particle size distribution of this surface-treated product is shown in Fig. 3 on a volume basis. Next, when screen printing was performed using a mask film in which the same print pattern as in Example 1 was formed using silver paste B6, clogging occurred in the mask portion, and it was impossible to print fine lines. Further, a solid print having a thickness of 50 m was carried out in the same manner as in Example 1, and this printed coating film was dried at 150 ° C. for 5 minutes. Thereafter, the volume resistance of the dried coating film was measured after being placed in an oven at 160 ° C. and 250 ° C. for 60 minutes. After drying, the volume resistance after placing in an oven at 160 ° C and 250 ° C for 60 minutes showed 2.5 Ε + 01 Ω'cm and 2.2E- 05 Ω'cm, respectively. In addition, the volume resistance of the dried coating film in the oven decreased with time. Figure 4 shows the decrease in volume resistance when the oven temperature is 250 ° C.

[0079] (Comparative Example 2)

In the same manner as in Example 1, except that 0.5 g of NO, Itenol NF 13 (Daiichi Kogyo Seiyaku Co., Ltd.) was used as a high-purity emulsifying dispersant in place of the surfactant in Example 1. As a result, 105 g of the silver powder dispersion (a6) and 50 g of the surface treated silver powder (b6) were obtained. This surface treatment The volume average particle size of the product was 1.5 μm, and the particle size distribution was such that the maximum particle size was 35 μm. Next, screen printing was performed using a mask film in which a print pattern was formed using silver paste B6 produced in the same manner as in Example 1. As a result, clogging occurred in a part of the mask, and it was impossible to print fine lines.

[0080] (Comparative Example 3)

 A silver powder was prepared in the same manner as in Example 1 except that 0.5 g of Boise 520 (manufactured by Kao Corporation) was used as a special carboxylic acid type polymer surfactant in place of the surfactant in Example 1. 105 g of the dispersion liquid (a7) and 50 g of the surface-treated silver powder (b7) were obtained. This surface-treated product had a volume average particle size of 0.9 μm and a particle size distribution with a maximum particle size of 24 μm. Next, screen printing was performed using a mask film in which a print pattern was formed using silver paste B7 produced in the same manner as in Example 1. As a result, clogging occurred in a part of the mask, and it was difficult to print fine lines.

 [0081] The silver powders and surfactants used in the examples and comparative examples are summarized in Table 1. Table 2 summarizes the values of volume resistivity, screen printing accuracy, and screen printing suitability when baked at 1 60 ° C and 250 ° C for 60 minutes.

 Here, screen printing accuracy and screen printability were evaluated according to the following criteria. (Screen printing accuracy)

 〇 and X were judged based on whether or not a conductive circuit pattern with a line width of 50 μm could be printed with screen printing.

 (Screen printing suitability)

 〇 and X were judged based on whether printing was possible without clogging by screen printing using a 400 mesh screen with a wire diameter of 18 / zm.

[0082] [Table 1] Table Ί

 [0083] [Table 2]

 Table 2

[0084] Table 1, Table 2 Karawaryokuru so the phosphoric acid ester surfactant phosphorus content is 0.5 to 10 weight _^0/0, or an alkyl amine and an alkyl amine salt-based surfactant When a conductive paste (silver paste) was prepared using the agent mixture, a conductive paste with good dispersibility was produced without clogging the mask for printing 30 m fine lines. In addition, the degree of dispersion and volume resistance of silver particles in the silver paste shown in Table 2, Fig. 3 and Fig. 4 As can be seen from the above, the dispersion state of the silver paste is higher than that of the agglomerated state in that the dispersed state can provide the closest packing, and the conductivity becomes higher immediately.

 Furthermore, it can be seen that when these conductive pastes use silver powder whose surface is treated with silver oxide, good conductivity can be realized by forming a wiring pattern by low-temperature firing when silver powder having a small particle diameter is used.

Industrial applicability

 According to the present invention, fine-sized silver or silver-containing compound particles are well dispersed, and a conductive circuit having a good conductivity with a narrow line width is formed in which physical properties such as increase in viscosity are not changed over time. Since a possible silver paste can be provided, it is industrially useful.

Claims

The scope of the claims

 [1] Particle strength of silver or silver compound compound Alkylamine-based or alkylamine salt-based surfactant, or phosphate ester-based surfactant having a phosphorus content of 0.5 to 10% by mass A method for producing a surface-treated silver-containing powder, characterized by having a step of freeze-drying a dispersion liquid dispersed in a dispersion solvent.

[2] The surface treatment according to claim 1, further comprising a step of dispersing particles of silver or a silver compound in the dispersion solvent in the presence of the surfactant in order to prepare the dispersion. A method for producing a silver-containing powder.

[3] The surface-treated silver-containing powder according to claim 2, wherein the silver or silver compound particles used as a raw material when the dispersion is prepared are silver or silver compound powders. Production method.

[4] In order to prepare the dispersion liquid, silver or silver compound particles are synthesized in a liquid phase, the synthesized particles are removed by filtration, and the dispersion solvent is dried before the removed particles are dried. The method for producing a surface-treated silver-containing powder according to claim 1, further comprising a step of adding the surfactant to the dispersion after being dispersed therein.

[5] The method for producing a surface-treated silver-containing powder according to claim 1, wherein the volume average particle diameter of the silver or silver compound particles is 0.05 to 10 μm.

[6] The surface-treated particle according to claim 1, wherein the silver or silver compound particles are silver particles whose surfaces are coated with silver oxide, and the silver oxide content is 1 to 30% by mass. A method for producing silver-containing powder.

 [7] A silver paste containing the surface-treated silver-containing powder obtained by the method for producing a surface-treated silver-containing powder according to any one of claims 1 to 6 as a main component.